The present invention relates to a disk drive apparatus,and more particularly to a disk drive apparatus where an optical pickup jumps over a track or tracks of a disk and performs a search operation.
Information signals are recorded on tracks of disks in a disk drive apparatus in a pattern of concentric circles or a spiral shape. The information signals that were recorded on the disk are read by an optical pickup that traces those tracks. In the disk drive apparatus an actuator of the optical pickup is driven to control the optical pickup. The optical pickup emits a light beam to a required track on the disk and reads the information signal by tracing that track. When the optical pickup is to be moved to a required track, the light beam emitted from the optical pickup traverses or jumps over one or a plural number of tracks. This operation is called a track jump in this specification. When the light beam is required to jump over tracks, the actuator controls the angle of the light beam emitted from a light source in the optical pickup.
When the light beam performs the track jump from a track TR1 to a track TR2 as shown in FIG. 1A an operation in the conventional art will be described in conjunction with FIG. 1B. When the light beam which traces the track TR1 under a known tracking servo is to jump to the track TR2, a constant positive jumping voltage is applied to a tracking coil of the actuator at a time point `a` as shown in FIG. 1B. The light beam thus starts to move laterally from a position `b` on the track TR1 towards the track TR2 as shown in FIG. 1A. When the light beam reaches a position `c` (FIG.1 A) on a border line of the contiguous tracks TR1 and TR2, at the time point `d` in FIG. 1B, the voltage applied to the tracking coil of the actuator is switched to a constant negative braking voltage as shown in FIG. 1B. This negative braking voltage causes the actuator to perform a braking operation for the actuator, and therefore the light beam stops its lateral movement when the light beam reaches a position `e` on the track TR2. The applying of braking voltage to the tracking coil is thus ceased at a time point `f`.
The track jump of the light beam from the track TR1 to the track TR2 is performed by the above described operation, and thereafter the light beam traces the track TR2. As the light beam traces the track TR2, as is well known, a tracking servo voltage is applied to the tracking coil.
When the light beam jumps from the track TR2 to an adjacent track TR3, as shown in the right portion in FIGS. 1A and 1B, the same operation as described above is performed.
In this conventional disk drive apparatus a drive voltage having a constant positive and negative waveform as shown in FIG. 1B is applied to the actuator when the track jump is to be performed. Accordingly, when another disk is set in the disk drive apparatus to read information signals on the disk, the characteristics of the actuator are inevitably changed by alterations due to the time passage and the temperature change between the disk which was previously set and the other disk which is newly set. Changes in the characteristics of the actuator cause changes in the jumping time, and cause instability in the track jumping. In addition, depending upon the position of the disk, differences in the track jumping conditions may cause differences in the jumping time, depending upon a position on the disk. Therefore, the reproducing operations of signals from the disk also become unstable.